c:\Program Files, like every other program since Windows 95.

And technically you should just use the 'ProgramFiles' environment variable, since the folder might be called something else if your install is in another language.

And Windows allows side-by-side installs of 64- and 32-bit versions of the same software; so installers should be aware of 'C:\Program Files (x86)' and 'C:\Program Files'; the first is for 32-bit programs on 64-bit machines.

This is just wrong. See

http://news.ycombinator.com/item?id=5176817

As a followup, what is supposed to go into C:\? I've always thought it was awful that Python gets installed into that directory.

I don't think that the user or an installer should put anything directly in C:\. I agree, it is awful that python goes there.

It's the same as going "I'll just save this folder on / so I don't have to remember the path later".